Disallow subtyping between T and U in T: Unsize<U>.

Author: eddyb

src/librustc/traits/select.rs

@@ -2461,7 +2461,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 let new_trait = tcx.mk_dynamic(
                     ty::Binder(tcx.mk_existential_predicates(iter)), r_b);
                 let InferOk { obligations, .. } =
-                    self.infcx.sub_types(false, &obligation.cause, new_trait, target)
+                    self.infcx.eq_types(false, &obligation.cause, new_trait, target)
                     .map_err(|_| Unimplemented)?;
                 self.inferred_obligations.extend(obligations);
 
@@ -2520,7 +2520,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             // [T; n] -> [T].
             (&ty::TyArray(a, _), &ty::TySlice(b)) => {
                 let InferOk { obligations, .. } =
-                    self.infcx.sub_types(false, &obligation.cause, a, b)
+                    self.infcx.eq_types(false, &obligation.cause, a, b)
                     .map_err(|_| Unimplemented)?;
                 self.inferred_obligations.extend(obligations);
             }
@@ -2583,7 +2583,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 });
                 let new_struct = tcx.mk_adt(def, tcx.mk_substs(params));
                 let InferOk { obligations, .. } =
-                    self.infcx.sub_types(false, &obligation.cause, new_struct, target)
+                    self.infcx.eq_types(false, &obligation.cause, new_struct, target)
                     .map_err(|_| Unimplemented)?;
                 self.inferred_obligations.extend(obligations);
 

src/test/compile-fail/issue-40288-2.rs

@@ -0,0 +1,41 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn prove_static<T: 'static + ?Sized>(_: &'static T) {}
+
+fn lifetime_transmute_slice<'a, T: ?Sized>(x: &'a T, y: &T) -> &'a T {
+    let mut out = [x];
+    //~^ ERROR cannot infer an appropriate lifetime due to conflicting requirements
+    {
+        let slice: &mut [_] = &mut out;
+        slice[0] = y;
+    }
+    out[0]
+}
+
+struct Struct<T, U: ?Sized> {
+    head: T,
+    _tail: U
+}
+
+fn lifetime_transmute_struct<'a, T: ?Sized>(x: &'a T, y: &T) -> &'a T {
+    let mut out = Struct { head: x, _tail: [()] };
+    //~^ ERROR cannot infer an appropriate lifetime due to conflicting requirements
+    {
+        let dst: &mut Struct<_, [()]> = &mut out;
+        dst.head = y;
+    }
+    out.head
+}
+
+fn main() {
+    prove_static(lifetime_transmute_slice("", &String::from("foo")));
+    prove_static(lifetime_transmute_struct("", &String::from("bar")));
+}

src/test/compile-fail/issue-40288.rs

@@ -0,0 +1,30 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn save_ref<'a>(refr: &'a i32, to: &mut [&'a i32]) {
+    for val in &mut *to {
+        *val = refr;
+    }
+}
+
+fn main() {
+    let ref init = 0i32;
+    let ref mut refr = 1i32;
+
+    let mut out = [init];
+
+    save_ref(&*refr, &mut out);
+
+    // This shouldn't be allowed as `refr` is borrowed
+    *refr = 3; //~ ERROR cannot assign to `*refr` because it is borrowed
+
+    // Prints 3?!
+    println!("{:?}", out[0]);
+}